1. Field of the Invention
This invention relates to an improvement of an apparatus for displaying a sample image, in which a continuous area corresponding to a morphological part of a sample, which is enlarged using a scanning electron microscope, a transmission electron microscope, a tunnel scanning microscope, or the like, and a micro-discrete area corresponding to a particular part of the sample are displayed in a superimposed condition relative to each other.
2. Prior Art
Heretofore, there has been known a sample image displaying apparatus for displaying an image of a sample in an enlarged scale using a scanning electron microscope (SEM), a transmission electron microscope (TEM), a tunnel scanning microscope (STM). For example, the scanning electron microscope scans an electron ray as charged particles on a sample surface (the terms "irradiation ray" used herein includes charged particles).
The sample image displaying apparatus includes an electron detection portion as a first detection portion, and a light receiving portion as a second detection portion. The electron detection portion is operated to detect a secondary electron or reflection electron produced by scanning of the electron ray. In accordance with the detection signal coming from the electron detection portion, dark and faint, white and black image signals are formed. Then, an image of the continuous area corresponding to the morphological structure of the sample is formed by the dark and faint, white and black image signals. At this time, a particular part of the sample is, in some cases, stimulated (cathodeluminescence) by irradiation of the electron ray. The light receiving portion receives that cathodeluminescence. For example, in the case where the sample is a mitochondrion of a biological cell, a continuous area image 1 is displayed as a morphological sample image such as the contour of the cell, the boundary of the cell, or the like by detection of the secondary electron or reflection electron (see FIG. 10). At the same time, by receiving the cathodeluminescence of a cholesterol caused by irradiation of the electron ray, there can be obtained a color image signal corresponding to a luminous part 2a of the sample (see FIG. 11). By this color image signal, a color image 2 as a micro-discrete area is displayed.
Heretofore, the continuous area image 1 obtained by bombarding of an electron ray, and the color image 2 obtained by a photoluminescence are separately taken in photographs, and the continuous area image 1 and the color image 2 are placed side by side for comparison in order to identify the illumination part of the sample.
Therefore, it is difficult to obtain a corresponding relation between each part of the continuous area image 1 of the sample and the luminous part 2a of the sample in such cases that the continuous area image 1 is complicated in shape and the cathodeluminescence is faint. Particularly, if the power is increased, a bombarding quantity of the electron ray is increased. Therefore, when the sample is a biological material, the chemical bond of polymer is disconnected by bombardment with the electron ray and as a result, discoloration occurs. Moreover, the cathodeluminescence becomes extremely faint, and the luminous area is difficult to be identified when the sample of a biological material is observed with high power. In other words, it is difficult to recognize the distribution of minor components which are contained in the sample.
In view of the above, the present applicant previously filed a Japanese Patent Application No. Hei 4-130966 under the title of "apparatus for morphological observation of a sample", in which the continuous area image 1 and the luminous part 2a of the color image 2 are displayed in a superimposed condition relative to each other.
However, in the case where the continuous area image 1 and the luminous part 2a of the color image 2 are displayed in a superimposed condition relative to each other, if the luminous part 2a is on the order where the luminous part 2a can be displayed by one pixel, the extremely faint luminous part 2a that can be displayed by one pixel or so, is buried in the continuous area image 1. Therefore, it is practically impossible to recognize the luminous part of the continuous area image 1. The reason is that the continuous area image 1 which is to be displayed in a colorless condition, originally has the color components of R, G and B.